<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	
	<title>Document</title>
	<style type="text/css">
		.box{
			color: red !important;
		}
/* 		#content .main_content h2{
	color: blue;
} */
		#content .main_content h2{
						
		}

		#content .main_content h2{
			color: red;
		}

	</style>
</head>
<body>
	<div class="box" style="color: blue">
		这是一个div元素
	</div>
	<div id="content">
		<div class="main_content">
			<h2>这是一个h2的标题</h2>
		</div>
	</div>

</body>
</html>